The viability and functional reserve of the corneal endothelium is of paramount importance in maintaining the normal transparency of the human cornea. At present, no clinically practical method exists of determining endothelial viability and functional reserve. This situation inhibits the development of better methods for the prevention and treatment of corneal disease, and the development of improved methods for preserving donor corneas for use in corneal transplant surgery. Corneal cryopreservation, i.e., preserving corneas in the frozen state, is potentially the best method for preserving donor corneas--it would allow corneas to be preserved for long periods and to be easily transported through-out the country as needed. Cryopreservation, although proven effective under optimum conditions, has fallen into disrepute largely because of the complexity of the currently available procedures, the requirement of having a reliable and highly skilled technician available on request at all times, and the absence of a method for evaluating the viability and functional reserve of the endothelium prior to surgery. In this application we propose to develop a clinically useful, non-invasive and non-destructive method for the evaluation of the viability of the human cornea. The method will evaluate both excised and in situ corneas (in the ennucleated globe and in the living patient) and will be applicable to the laboratory, the operating suite, and the clinic. The method will be used to evaluate the suitability of donor corneas for transplantation and to evaluate endothelial changes resulting from disease, trauma, and treament. We also propose to develop and refine a practical and acceptable method of corneal crypreservation. The evaluation method will be used to determine the viability of the cryopreser ed donor cornea in the immediate pre-operative period.